Mask set for measuring an overlapping error and method of measuring an overlapping error using the same

ABSTRACT

A mask set for measuring an overlapping error according to the invention comprises a first mask consisted of a mask substrate on which a plurality of unit patterns are formed: The plurality of unit patterns are arranged in radial shape round a given center. The mask set of the present invention further comprises a second mask consisted of a mask substrate on which a plurality of unit patterns are formed. The plurality of unit patterns of the second mask are arranged in same shape as the plurality of unit patterns of the first mask, whereby when the first and second masks are overlapped to each other, the unit pattern of the first mark and the neighboring unit pattern of the second mask maintains a certain angle.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mask set for measuring an overlappingerror and method of measuring an overlapping error using the same. Inparticular, the present invention relates to a mask set for measuring anoverlapping error and method of measuring an overlapping error which canidentify an degree of overlapping error generated in all directionsduring the photolithography developing process and also can easilydetermine whether an overlapping error occurs or not even using amicroscope having a low magnifying power.

2. Description of the Prior Art

As the integration of the semiconductor device becomes higher andsmaller, the degree of overlapping alignment between an underlying layerand an upper layer or between an underlying layer and an impuritydiffusion layer becomes an important factor in reliability of thedevice. Accordingly, a mask, on which a mark for measuring anoverlapping error is formed, is commonly used to measure the degree ofoverlapping alignment.

FIG. 1 shows a conventional mask for measuring an overlapping error.

The mask for measuring an overlapping error is consisted of mainpatterns 1 and sub patterns 2 formed in the upper and underlying layerThese patterns can measure an overlapping error created in only onedirection of the X-axis or Y-axis direction. However, in case that anoverlapping error created in both directions is measured, a measureoperation are performed twice by this pattern. In addition, when amicroscope having a high magnifying power is used and the patternsbecome more fined, a measuring error occurs frequently due to aberrationof a lens and difference of a measuring point (eye) and a determiningpoint of the measuring scale. Accordingly, although dedicatedmeasurement equipments has been developed, there are problems that theyare expensive in cost and a processing time is delayed.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a mask set formeasuring an overlapping error which can identify an overlapping errorgenerated not only in the X-axis and Y-axis directions but also in alldirections during the photolithography developing process and also caneasily determine an overlapping error even using a microscope having alow magnifying power.

To achieve these objects, a mask set for measuring an overlapping erroraccording to the invention comprises a first mask consisted of a masksubstrate on which a plurality of unit patterns are formed. Theplurality of unit patterns are arranged in radial shape round a givencenter.

The mask set of the present invention further comprises a second maskconsisted of a mask substrate on which a plurality of unit patterns areformed. The plurality of unit patterns of the second mask are arrangedin same shape as the plurality of unit patterns of the first mask,whereby when the first and second masks are overlapped to each other,the unit pattern of the first mark and the neighboring unit pattern ofthe second mask maintains a certain angle.

A method of measuring an overlapping error according to the presentinvention comprises the steps of forming first measuring patterns on awafer using a first mask on which a plurality of unit patterns arearranged in radial shape round a given center; forming overlappingsecond measuring patterns on said wafer using a second mask on which aplurality of unit patterns are arranged in same shape as the pluralityof unit patterns of the first mask, whereby the first measuring patternsformed by the first mask and the second measuring patterns formed by thesecond mask maintains a certain angle; identifying an overlapping errorbetween the first measuring patterns and said second measuring patterns;calculating a value of the overlapping error.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the present invention will be understoodby reading the detailed explanation of the embodiment with reference tothe accompanying drawings in which:

FIG. 1 shows a conventional pattern for measuring an overlapping error.

FIG. 2 is a plan view of a first mash for measuring an overlapping erroraccording to the present invention.

FIG. 3 is a plan view of a second mask for measuring an overlappingerror according to the present invention.

FIG. 4A to FIG. 4C show the shape of the measuring patterns formed on awafer when the first and second mask according to the present inventionare applied.

FIG. 5A illustrates the principles of calculating a value of anoverlapping error.

FIG. 5B is a detail view of a portion of 5A in FIG. 5A

FIG. 6A shows measuring guides for identifying the measuring patterns.

FIG. 6B is a detail view of a portion of 6A in FIG. 5A.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 is a plan view of a first mask for measuring an overlapping erroraccording to the present invention.

A first mask 10 is consisted of a plurality of unit patterns 12 whichare formed on a mask substrate 11. The plurality of unit patterns 12 areextended radially round a give center. Two unit patterns 12 which areadjacent from each other form an angle of 2θ₁.

FIG. 3 is a plan view of a second mask for measuring an overlappingerror according to the present invention.

A second mask 20 is consisted of a plurality of unit patterns 22 whichare formed on a mask substrate 21. The plurality of unit patterns 22 areextended radially round a give center. Two unit patterns 22 which areadjacent from each other form an angle of 2θ₁.

In the first or second masks 10 or 20, an angle of 2θ₁ between theneighboring unit patterns 12 or 22 is in the range between 0° and 90° .The unit patterns 12 and 22 are a dark pattern made of materials such aschrome or a clear pattern such as quartz forming a mask substrate.

When the first and second masks 10 and 20 are overlapped to each other,an angle between the one unit pattern 12 of the first mark 10 and theneighboring unit pattern 22 of the second mask 20 is θ₁. That is, anangle between the one unit pattern 12 of the first mask 10 and theneighboring unit pattern 22 of the second mask 20 is in the rangebetween 0° and 45°.

FIG. 4A to FIG. 4C show the shapes of the measuring patterns formed on atest wafer when a lithography process is performed by means of the firstand second mask for measuring an overlapping error according to thepresent invention. In FIG. 4A, FIG. 4B and FIG. 4C, first measuringpatterns 110 are formed on the test wafer by the first mask 10, andsecond measuring patterns 210 are formed on the test wafer by the secondmask 20 in overlapped state.

FIG. 4A shows that the measuring error does not occurred, FIG. 4B showsthat the measuring error occurs in direction of Y axis. And, FIG. 4Cshows that the measuring error occurs in direction of X axis.

These measuring patterns 110 and 210 are noticeable through a microscopehaving a low magnifying power or a baked eye depending on the case. Whentwo measuring patterns 110 and 210 are overlapped, they are greatlydistorted in shape even for a fine overlapping error, therefore, itpossible to easily identify an overlapping error. Additionally,deviation toward the X-axis and Y-axis direction or any direction can bealso identified by shape of ellipse.

As shown in FIG. 4B and FIG. 4C, in case that an overlapping erroroccurs, the methods of calculating a value of the overlapping error andcompensating will be explained as follows.

FIG. 5A is a view for illustrating the principles of calculating a valueof the overlapping error when the measuring patterns are deviated indirection of the Y-axis as shown in FIG. 4B, and FIG. 5B is a detailview of a portion of 5A in FIG. 5A.

A value of overlapping error is measured at the line of apsides of theellipse in which two measuring patterns 110 and 210 are overlapped, andis calculated by the following Equation 1:Δy=Δr·tan θ₂   (1)

When the first and second measuring patterns are deviated in directionof the X-axis as shown in FIG. 4C, a value of the overlapping error iscalculated by the following Equation 2;Δx=Δr·tan θ₂   (2)wherein; Δx and Δy are values of actual overlapping error,

-   -   Δr is a distance from a central point of a circle to a cross        point of the patterns 110 and 210; and    -   θ₂ is a deviation angle of the first and second measuring        patterns 110 and 210.

Meanwhile, as the unit patterns 12 and 22 of the first and second masks10 and 20 have a same shape, it is actually difficult to identify themeasuring patterns 110 and 210. Therefore, the first and secondmeasuring guides 12 and 22 are formed on the unit patterns 12 and 22 ofthe first and second masks 10 and 20, respectively in order to identifythe first and second measuring patterns 110 and 220.

At this time, the each first measuring guide 12 is formed on a left sideof the each unit pattern 12 of the first mask 10, and the each secondmeasuring guide 22 is formed on a right side of the each unit pattern 21of the second mask 20, as shown in FIG. 6A and FIG. 6B. Therefore, theeach first measuring guide 12 formed on the each unit pattern 12 and theeach second measuring guide 22 formed on the each unit pattern 21 arefaced each other.

As a result of the measurement, if the deviation degree of θ₂ of thefirst and second measuring patterns 110 and 210 is 2.5°, the secondmeasuring pattern 210 is deviated in direction of Y-axis, and thedistance Δr between the center and the cross point of the first andsecond measuring patterns 110 and 210 is 1.5 μm, a value of theoverlapping error Δy can be defined as follows: $\begin{matrix}{{\Delta\quad y} = {1.5\quad\mu\quad m \times \tan\quad 2.5{^\circ}}} \\{= {0.0655\quad\mu\quad{m\quad\lbrack + \rbrack}}}\end{matrix}$

According to the present invention, an overlapping error can easilyidentified by a microscope or by a baked eye. Also, the overlappingerrors generated in a directions of Y-axis and X-axis can be measuredsimultaneously.

The foregoing description, although described in its preferredembodiments with a certain degree of particularity, is only illustrativeof the principle of the present invention. It is to be understood thatthe present invention is not to be limited to the preferred embodimentsdisclosed and illustrated herein. Accordingly, all expedient variationsthat may be made within the scope and spirit of the present inventionare to be encompassed as further embodiments of the present invention.

1. A mask set for measuring an overlapping error, comprising: a firstmask consisted of a mask substrate on which a plurality of unit patternsare formed, said plurality of unit patterns arranged in radial shaperound a given center; a second mask consisted of a mask substrate onwhich a plurality of unit patterns are formed, said plurality of unitpatterns arranged in same shape as said plurality of unit patterns ofsaid first mask, whereby when said first and second masks are overlappedto each other, said unit pattern of said first mark and the neighboringunit pattern of said second mask maintains a certain angle.
 2. The maskset of claim 1, said some one unit pattern and neighboring unit patternof said unit pattern of the said first mask maintains an angle ofbetween 0° and 90°.
 3. The mask set of claim 1, said some on unitpattern of said first mark and the neighboring unit pattern of saidsecond mask maintains an angle of between 0° and 45°.
 4. The mask set ofclaim 1, said unit patterns are dark patterns.
 5. The mask set of claim1, said unit patterns are clear patterns.
 6. The mask set of claim 1,said each unit pattern of said first mask and said each unit pattern ofthe second mask have a measuring guide, respectively, whereby the firstand second measuring patterns formed by said first and second masks canbe easily distinguished.
 7. The mask set of claim 6, said each measuringguide formed on said each unit pattern of said first mask and eachmeasuring guide formed on said each unit pattern of said second mask arelocated at opposite portions, whereby said each measuring guide formedon said each unit pattern of said first mask and said each measuringguide formed on said unit pattern of said second mask are faced eachother.
 8. A method of measuring an overlapping error, comprising thesteps of: forming first measuring patterns on a wafer using a first maskon which a plurality of unit patterns are arranged in radial shape rounda given center; forming overlapping second measuring patterns on saidwafer using a second mask on which a plurality of unit patterns arearranged in same shape as said plurality of unit patterns of said firstmask, whereby said first measuring patterns formed by said first maskand said second measuring patterns formed by said second mask maintainsa certain angle; identifying an overlapping error between said firstmeasuring patterns and said second measuring patterns; calculating avalue of the overlapping error using the equations 1 and 2Δx=Δr·tan θ₂   [equation 1]Δx=Δr·tan θ₂   [equation 2] wherein; Δx and Δy are actual value ofoverlapping error Δr is a distance from a central point to a cross pointof said first and second measuring patterns; and θ₂ is a deviation angleof the first and second measuring patterns.
 9. The method of claim 8,said some one unit pattern and neighboring unit pattern of said unitpattern of the said first mask maintains an angle of between 0° and 90°.10. The method of claim 8, said some on unit pattern of said first markand the neighboring unit pattern of said second mask maintains an angleof between 0° and 45°.
 11. The method claim 8, said unit patterns aredark patterns.
 12. The method claim 8, said unit patterns are clearpatterns.
 13. The method claim 8, said each unit pattern of said firstmask and said each unit pattern of the second mask have a measuringguide, respectively, whereby the first and second measuring patternsformed by said first and second masks can be easily distinguished. 14.The method of claim 13, said each measuring guide formed on said eachunit pattern of said first mask and each measuring guide formed on saideach unit pattern of said second mask are located at opposite portions,whereby said each measuring guide formed on said each unit pattern ofsaid first mask and said each measuring guide formed on said unitpattern of said second mask are faced each other.